Lateral Medullary Syndrome (Wallenberg Syndrome)

Etiology

LMS is most commonly caused by an acute ischemic stroke affecting the dorsolateral medulla, due to a thrombus or embolism of the VA or PICA. Less common causes include injury to the VA in the neck, dissection, arteriovenous malformation, or arteritis. The most important risk factors for LMS are hypertension, diabetes, and cigarette smoking. The common etiologies of LMS are as follows:

• Atherosclerotic disease: This is typically due to thromboembolism or, less commonly, hemodynamic insufficiency.
• Cardiogenic embolism: This is associated with atrial fibrillation,[6] mechanical heart valves, intracardiac thrombi, dilated cardiomyopathy, myocardial infarction, and infective endocarditis. Cocaine misuse, neck manipulation, medullary tumors, radiation necrosis, and hematomas may also lead to embolism.
• VA dissection: This is particularly seen in younger individuals presenting with headache and neurological symptoms consistent with LMS.[7] 
• Hypoplastic VA: This is a rare cause, especially if additional risk factors are present in younger patients.[8] 
• Surgical trauma: PICA is often exposed and injured during surgeries, especially telovelar approaches.[9]
• Arteriovenous malformation and aneurysms: This is a common cause of LMS, especially involving the PICA.
• Vertebrobasilar dolichoectasia and ectatic PICA: These malformations compress the medulla and cranial nerves, causing neurovascular compression syndromes.[9]
• Connective tissue diseases: Ehlers-Danlos syndrome, Marfan syndrome, and fibromuscular dysplasia, can weaken the walls of blood vessels.

Less common causes include subclavian steal syndrome, rotational vertebral artery compression syndrome, Fabry disease, mitochondrial encephalopathy, lactic acidosis, and migraines.[10][11]

Epidemiology

Posterior circulation strokes represent about 20% of all ischemic strokes. In a 2024 registry of more than 2900 strokes, posterior circulation strokes accounted for 28.8%, with LMS representing 12%.[12] Notably, lateral medullary infarcts occur more frequently in those who consume alcohol.[13] Angiography showing VA involvement is more common (67%) than isolated PICA involvement (10%). PICA-related infarcts are often due to cardiogenic embolism.[8] Between 51% and 94% of patients with lateral medullary syndrome experience some degree of dysphagia.[1][3]  

Pathophysiology

Large artery atherothrombosis accounts for nearly 75% of LMS cases, followed by cardioembolism in 17%, and VA dissection in 8%.[4] Pathophysiologically, the clinical features of LMS correlate with the affected structures in the dorsolateral medulla, an area supplied by the PICA, a branch of the VA (see Image. Anatomy of Brain Vascular Territories). Therefore, LMS is commonly caused by occlusion of the VA. Clinical features of LMS are correlated with dysfunction of neuroanatomical structures as outlined below:

• Vestibular nuclei: Dizziness, vertigo, nystagmus, skew deviation, nausea, and vomiting
• Spinocerebellar tracts and the inferior cerebellar peduncle: Ipsilateral ataxia and lateral pulsion [1][3][8]
• Caudal trigeminal nucleus and tract: Ipsilateral facial sensation abnormalities, primarily involving pain and temperature
• Spinothalamic tract: Contralateral pain and temperature loss affecting the arm, body, and leg
• Descending sympathetic fibers: Ipsilateral Horner syndrome
• Nucleus ambiguus: Ipsilateral dysphagia, dysarthria, and dysphonia [8][14] 
  • Cough reflex may also be impaired.[3] 
• Nucleus and tractus solitarius: Ipsilateral taste impairment

A 2025 prospective flexible endoscopic evaluation of swallowing and high-resolution pharyngeal manometry study demonstrated severe pharyngeal sensory loss and delayed swallow initiation in medullary strokes compared with cerebellar strokes.[15]  Hyponatremia after a brain injury occurs due to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and cerebral salt wasting syndrome. SIADH has been reported in patients with lateral medullary infarction. The proposed pathophysiology involves failure of nonosmotic stimuli to propagate from the carotid sinus via the vagus nerve due to a lesion in the nucleus tractus solitarius of the medulla. This lesion causes the disinhibition of antidiuretic hormone secretion by the pituitary gland, causing SIADH.[16]

Other clinical findings are rarer but have corresponding anatomical variations. Ipsilateral hemiparesis (Opalski variant) has been attributed to LMS affecting the lateral medulla, caudal to the corticospinal decussation, as discussed in a 2024 case report.[17] Life-threatening bradycardia precipitated by vertebral dissection-related LMS has also been reported.[18] Moreover, persistent hiccups are believed to result from the involvement of the nucleus ambiguus or adjacent respiratory regulatory centers.

History and Physical

Many patients with LMS are older adults with multiple vascular risk factors. Typical symptoms include acute onset of vertigo, dizziness, nystagmus, ataxia, nausea, vomiting, dysphagia, hiccups, dysphonia, facial pain, visual disturbances, and headaches. Sensory signs and symptoms are the most frequent manifestations (96%). Ipsilateral limb ataxia, Horner syndrome, and sensory impairments are also common. Less common clinical presentations include dysarthria, skew deviation, oscillopsia due to nystagmus, and ipsilateral lateral pulsion.

Gradual onset occurs in approximately 25% of cases, progressing over several hours to days, with symptoms of headache, dizziness, vertigo, or gait ataxia, followed by sensory deficits, hiccups, hoarseness, and dysphagia. Weakness is a relatively uncommon feature of LMS, often resulting in a missed diagnosis. Partial syndromes are also more common than complete syndromes [1][2][8][10][16]

Classic signs of LMS include:

• Impairment of pain and thermal sensation over the contralateral side of the trunk and limbs
• Impairment of pain and thermal sensation over the ipsilateral face
• Ipsilateral Horner syndrome (partial ptosis, miosis, and facial anhidrosis)
• Ipsilateral limb ataxia
• Ipsilateral taste impairment 
• Dysphagia
• Nystagmus,
  • This may be horizontal or horizontal–rotational, beating opposite to the side of the lesion, or directionally changing gaze-evoked, is often accompanied by skew deviation.
• Intractable hiccups (may lead to diagnostic delay)

The clinical presentation varies depending on the size and location of the infarct.[4]

Evaluation

Evaluating patients with LMS should include a detailed clinical history, physical examination, and appropriate testing, including:

• Screening of stroke risk factors such as hypertension, diabetes mellitus, smoking history, and heart disease. A history of neck pain, trauma, or headache, particularly in younger patients, may suggest vertebral artery dissection (see Image. Vertebral Anatomy in Neck Region).[8][11]
• A complete neurological examination is critical because LMS is a clinical diagnosis based on a characteristic history and a constellation of physical findings.
• Routine blood testing, including blood glucose and serum electrolytes, is appropriate.
• An electrocardiogram is necessary to screen for atrial fibrillation.
• Transthoracic echocardiography with Doppler and neck imaging, such as carotid ultrasound or computed tomography (CT)/magnetic resonance (MR) angiography.
• Clinical and instrumental swallowing evaluations can assess swallowing, which are carried out by videofluoroscopy and/or fiberendoscopic examination.[3]

Diagnostic Imaging Tests

A CT scan of the brain is typically the initial imaging test for patients with lateral medullary syndrome, as with any emergent evaluation for a patient with acute ischemic stroke symptoms. However, CT gives suboptimal visualization of the posterior fossa structures due to obscuration by bony structures. Early ischemic changes are often not visible.[11] Magnetic resonance imaging (MRI) of the brain provides better visualization of the soft tissue structures. For example, an imaging protocol that includes fluid attenuation inversion recovery sequences improves the visualization of medullary infarction.[8][10] Additionally, diffusion-weighted MRI can detect an infarct earlier.

Neurovascular Studies

CT angiography and MR angiography examinations are advanced imaging studies that may be clinically indicated, often in consultation with a neurologist. 

Treatment / Management

Similar to the management of any acute ischemic stroke, the principle of "time is brain" underscores the need for rapid evaluation. An algorithmic approach should be developed within each hospital.[19] Management in certified stroke centers has been shown to improve overall patient outcomes.[20] Treatment aims to reduce the size of the infarction and prevent any medical complications to improve patient outcomes and prognosis.[4]

Standard acute ischemic stroke algorithms apply, including intravenous thrombolysis, blood pressure control, and antiplatelet/anticoagulation (see Image. Blood Supply to Medulla). Intravenous fibrinolytic therapy with alteplase or tenecteplase is indicated for LMS due to acute ischemic infarction within 4.5 hours of onset.[19] Intravenous fibrinolytic treatment is also indicated for an acute stroke of unknown onset if the MRI shows an infarct in the diffusion-weighted image but a negative fluid-attenuation inversion recovery sequence image.[21] 

Thrombectomy for large vessel occlusion in the anterior circulation can be efficacious up to 24 hours from the onset (see Image. Diagram of Brain Circulation). The outcomes with thrombectomy for posterior circulation large vessel occlusion, including the VA and basilar artery, are mostly uncertain.[21] These patients should be treated at certified stroke centers with interventional neuroradiologists and receive individualized treatment plans to achieve the best outcomes.[22]

Acute management of LMS also includes the following:

• Intensive care monitoring should be used for respiratory failure and increased intracranial pressure.[13] Signs of increased intracranial pressure may include disorientation, lethargy, headache, and vomiting. Late signs include bradycardia, hypertension with widened pulse pressure, or an irregular respiratory pattern (Cushing triad). Treatment includes head elevation to 30°, blood pressure management to maintain cerebral perfusion, targeted hyperventilation, neurosurgical consultation, and occasionally osmotic agents (such as 3% saline or mannitol).[23]
• Extracranial VA stenting may be beneficial during endovascular therapy for tandem posterior circulation lesions. A 2025 registry analysis demonstrated improved 1-year functional outcomes with this intervention.[24]
• Secondary stroke prevention can be achieved with antiplatelets, antihypertensives, and statins.[11] 
• An enteral nutrition evaluation with nasogastric or gastrostomy feeding is useful if severe dysphagia persists.
• Dysphagia management can be achieved with postural/dietary modifications, swallowing exercises, or botulinum toxin for trismus.[1][3] Persistent dysphagia mandates early swallow assessment, enteral support, and goal-directed therapy with long-term rehabilitation.[25]
• Low-molecular-weight heparin prophylaxis is useful for deep vein thrombosis.
• Speech-language therapy can be effective.
• Gabapentin is useful for persistent hiccups or chronic facial pain.[2]
• Managing autonomic complications is essential; cardiac pacing can help with acute heart failure due to bradycardia.[26]
• An ophthalmology evaluation can be useful for neurotrophic keratopathy.[14]
• Regular evaluation of speech and motor function are essential.[10]
(B2)

Differential Diagnosis

Depending on the predominant symptoms, the differential diagnosis of LMS will vary. The most common presentation is dizziness and vertigo with nausea and vomiting. The most important differential diagnosis is acute peripheral vestibulopathy, or acute vestibular neuritis. A careful evaluation should differentiate the 2 using the head impulse-nystagmus-skew deviation (HINTS) test. The head impulse test is negative in LMS but positive in cases of peripheral vestibulopathy. Nystagmus is unilateral, away from the side of the lesion with vestibulopathy, but bilateral and/or vertical for LMS. Skew deviation is present in LMS but absent in peripheral vestibulopathy. The HINTS test may identify patients at risk for stroke who require MRI and hospitalization.[27] Hemorrhagic stroke is much less common, and headache is a prominent symptom. Acute demyelination, as in multiple sclerosis, may present with medullary symptoms, but the patients are generally younger women with a history of a demyelinating disease.[4]

Other differential diagnoses include:

• Headache (migraine or cluster)
• Intracerebral hemorrhage
• Brainstem or cerebellar tumor, including primary and secondary malignancies
• Psychiatric conversion disorders
• Reversible cerebral vasoconstriction syndrome [11]
• Vasculitis of the large and medium-sized vessels, such as giant cell arteritis
• Vertebral artery dissection

Prognosis

LMS generally has a favorable prognosis. Significant functional recovery is common, including improvement of dysphagia.[1][8]

Complications

Complications of LMS can include the following:

• Respiratory complications may include aspiration pneumonia, respiratory failure, and central hypoventilation syndrome (eg, Ondine curse). Respiratory failure due to autonomic dysfunction can be observed rarely and causes apnea and death. 
• Syndrome of inappropriate antidiuretic hormone can be a complication, although rare in LMS compared to other types of stroke.
• Neurotrophic keratopathy (corneal damage and infection) is a potential complication.[14][28]
• Severe dysphagia may occur in lateral medullary syndrome due to involvement of the nucleus ambiguus, which innervates muscles responsible for swallowing.
• Trigeminal neuralgia can result from disruption of the spinal trigeminal nucleus and tract, leading to facial pain and sensory disturbances.
• Cardiac complications are rare and may occur when the nucleus tractus solitarius, which is involved in cardiovascular regulation, is affected.[26]
• Obstructive hydrocephalus may develop as a rare complication of lateral medullary syndrome due to brainstem edema or infarct-related compression of cerebrospinal fluid pathways, such as the fourth ventricle.